Role of Serine Coordination in the Structural and Functional Protection of the Nitrogenase P-Cluster.

Nitrogenase catalyzes the multielectron reduction of dinitrogen to ammonia. Electron transfer in the catalytic protein (MoFeP) proceeds through a unique [8Fe-7S] cluster (P-cluster) to the active site (FeMoco). In the reduced, all-ferrous (P) state, the P-cluster is coordinated by six cysteine residues.

O Electron Nuclear Double Resonance Analysis of Compound I: Inverse Correlation between Oxygen Spin Population and Electron Donation.

Although the activation of inert C-H bonds by metal-oxo complexes has been widely studied, important questions remain, particularly regarding the role of oxygen spin population (i.e., unpaired electrons on the oxo ligand) in facilitating C-H bond cleavage.

Structure and Reactivity of a High-Spin, Nonheme Iron(III)- Superoxo Complex Supported by Phosphinimide Ligands.

Nonheme iron oxygenases utilize dioxygen to accomplish challenging chemical oxidations. A further understanding of the Fe-O intermediates implicated in these processes is challenged by their highly transient nature. To that end, we have developed a ligand platform featuring phosphinimide donors intended to stabilize oxidized, high-spin iron complexes.

Different Kinetic Reactivity of Electrons in Distinct TiO Nanoparticle Trap States.

Electrons added to TiO and other semiconductors often occupy trap states, whose reactivity can determine the catalytic and stoichiometric chemistry of the material. We previously showed that reduced aqueous colloidal TiO nanoparticles have two distinct classes of thermally-equilibrated trapped electrons, termed Red/ and Blue/ . Presented here are parallel optical and electron paramagnetic resonance (EPR) kinetic studies of the reactivity of these electrons with solution-based oxidants.

An efficient, step-economical strategy for the design of functional metalloproteins.

The bottom-up design and construction of functional metalloproteins remains a formidable task in biomolecular design. Although numerous strategies have been used to create new metalloproteins, pre-existing knowledge of the tertiary and quaternary protein structure is often required to generate suitable platforms for robust metal coordination and activity. Here we report an alternative and easily implemented approach (metal active sites by covalent tethering or MASCoT) in which folded protein building blocks are linked by a single disulfide bond to create diverse metal coordination environments within evolutionarily naive protein-protein interfaces.

Using an artificial tryptophan "wire" in cytochrome c peroxidase for oxidation of organic substrates.

Lignolytic peroxidases use an electron transfer (ET) pathway that involves amino acid-mediated substrate oxidation at the surface of the protein rather than at an embedded heme site. In many of these peroxidases, redox catalysis takes place at a substrate accessible tyrosine or tryptophan (Trp) amino acid. Here, we describe new mutants of cytochrome c peroxidase (CcP) that were designed to incorporate a Trp-based "wire" that can move oxidizing equivalents from the heme to the protein surface.

Photochemical proton-coupled C-H activation: an example using aliphatic fluorination.

Selective functionalization of unactivated C-H bonds is an ongoing chemical challenge. C-H activation requires the transfer of H and e, so called proton-coupled electron transfer (PCET) reactions. Recent efforts in photochemical PCET involving C-H bonds show great promise for the synthesis of new compounds.